1. Field of the Invention
The present invention relates to a radiographic imaging apparatus for radiographically imaging an object using radiation and a control method thereof.
2. Description of the Related Art
There is an apparatus conventionally known which irradiates a target object with radiation and detects the intensity distribution of radiation transmitted through the target object, thereby obtaining a radiographic image of the target object. Such an apparatus is widely used in industrial nondestructive inspection and medical diagnosis.
The shooting is commonly conducted by a film/screen method using radiation. This method enables shooting by combining a photosensitive film and a phosphor sensitive to radiation. In this method, sheets of a rare-earth phosphor that emit light when irradiated with radiation are held in tight contact with both sides of a photosensitive film. The phosphor converts radiation transmitted through an object into visible light. The photosensitive film captures the light. A latent image formed on the film is then developed into a visible image by chemical treatments.
Recent progress of digital technologies has popularized a scheme of converting a radiographic image into an electrical signal, processing the electrical signal, and reproducing it as a visible image on a CRT or the like, thereby obtaining a high-quality radiographic image. To convert a radiographic image into an electrical signal, a radiographic image recording/reproduction system has been proposed. This system temporarily accumulates an image of transmitted radiation in a phosphor as a latent image. The latent image is then photoelectrically read out by irradiating it with excitation light such as a laser beam and output as a visible image.
An apparatus for shooting a radiographic image using a semiconductor sensor has also been known along with recent advance in semiconductor process technologies. This system has a dynamic range much wider than that of a conventional radiographic system using photosensitive films and can obtain a radiographic image without being affected by variations in the exposure amount of radiation. The system can also immediately obtain an output image because no chemical treatment is necessary, unlike the conventional scheme using photosensitive films.
FIG. 12 is a schematic view showing a system using such a radiographic imaging apparatus.
A radiographic imaging apparatus 103 (to be abbreviated as an X-ray imaging unit hereinafter) incorporates a radiation detection sensor 104. Radiation emitted by a radiation generator 101 irradiates an object 102. The radiation transmitted through the object is converted into visible light via a phosphor and detected as an electrical signal by photoelectric conversion elements arrayed in a two-dimensional matrix. The system includes a control unit 105 which controls read drive of the radiation detection sensor 104 and image transfer. Under the control of the control unit 105, an image output from the X-ray imaging unit 103 undergoes digital image processing so that a monitor 106 displays a radiographic image of the object.
This system can advantageously monitor an image immediately, unlike the above-described radiographic image recording/reproduction system. In this system, the X-ray imaging unit is generally installed in a dedicated frame stationarily placed in a radiographic examination room to shoot an object in, as examples, a standing or lying position. Portable X-ray imaging units which have been developed in recent years also enable shooting at an arbitrary shooting posture. Japanese Patent Laid-Open No. 2005-000470 proposes a technique of stationarily supporting a portable X-ray imaging unit at a position opposing a tube and a technique of independently using it separated from the support portion. The former technique facilitates positioning so as to quickly perform accurate alignment. The latter technique that allows to place the X-ray imaging unit at an arbitrary position is applicable to an immovable object to reduce his/her burden. According to the techniques proposed in Japanese Patent Laid-Open No. 2005-000470, it is possible to implement two shooting forms by one apparatus and therefore improve the convenience.
However, when implementing the two different shooting forms by a single apparatus, there is also a problem to solve to optimize the apparatus for each form.
The medical field tends to be backward in prompting wireless communication for fear of interference between apparatuses, influence on pacemakers, and reliability of wireless communication. In fact, the above-described X-ray imaging unit also uses cables to supply power to the apparatus and transmit/receive information. When shooting the radiographic image using the X-ray imaging unit incorporated in a cassette, a human body gets on the apparatus in many cases. Hence, the cables which are led from a side surface not to make unevenness in the direction of thickness have a flexible structure in consideration of leading operability. On the other hand, when the X-ray imaging unit is supported in a frame, there is a high possibility that cable leading to a side surface of the apparatus impedes human body alignment and operations. In this case, the communication speed has priority over the flexibility of cables in the specifications.